1. Field of Invention
This invention relates generally to chemical anchors installable in a hole drilled in masonry in which is deposited a chemical bonding agent to fasten a fixture or other object to the surface of the masonry, and more particularly to a chemical anchor bolt and cap assembly in which the threaded shank of the bolt is coated with a releasable barrier layers making it possible to turn the bolt and thereby tighten or remove the fastening.
2. Status of Prior Art
The term masonry refers to a construction of stone or similar material such as concrete and brick. The walls, ceiling and floors of many edifices are formed of masonry. In order, therefore, to fasten fixtures, machines, structural members or other objects to masonry, a masonry anchor is required for this purpose.
In the case of concrete or other forms of masonry, one cannot drill a hole therein and then tap this hole so that it can receive an anchor bolt, a threaded stud or other threaded mounting means to secure a fixture or other object to the face of the masonry. The nature of masonry is such that a cutting action to cut female threading into the bank of the hole cannot be effected, for this action will disintegrate the masonry material.
In order, therefore, to anchor a threaded rod or stud in a hole drilled in masonry, the present practice is to use a curable chemical bonding agent for this purposes. The typical agent of this type has two flowable components, one being a resinous bonding agent, the other a hardener therefor. The resins may be phenol, vinyl, ester or epoxy based. The two components, when stored, must be separated to prevent interaction therebetween. Many bonding agents currently available have an accelerated curing time and set within 10 to 30 minutes to afford substantial holding power. In practice, a charge of the resinous component and sufficient hardener intermixed therewith are deposited in the hole, and a threaded mounting stud is then inserted in the hole.
To this end, use may be made of a dispenser gun to inject a charge of the flowable bonding agent into the drilled hole. Or the charge may be contained in a capsule that is deposited in the drilled hole and is ruptured to release the bonding agent when the stud is inserted in the hole.
After the resinous interfacial layer between the stud and the bank of the hole cures and rigidifies, it then bonds itself both to the stud and to the masonry whereby the stud is permanently anchored in the hole. In order now to secure a fixture to the masonry face, the fixture which has a mounting hole therein is placed onto the projecting stud and locked thereto by a washer and nut.
A chemical anchor in accordance with the invention is useable with any type of curable bonding agent capable of setting in a reasonable time. The term epoxy, as hereafter used, is intended to cover a two-component epoxy and any other suitable curable bonding agent.
The concern of the present invention is with a chemical anchor that makes use of a bolt from whose head extends an externally-threaded cylindrical shank coated with a release agent. When the shank of the bolt is inserted in a drilled masonry hole having a charge of an uncured bonding agent deposited therein the release coating prevents this bonding agent, when cured and hardened from adhering to the shank.
A chemical anchor of this type is disclosed in the Kellison U.S. Pat. No. 4,642,964 and also in the Roth U.S. Pat. No. 5,590,360. In the chemical anchors disclosed in these patents, when the bonding agent hardens in the drilled masonry hole, a female thread is then cast in the hardened epoxy surrounding the shank. This female thread mates with the male thread of the release-coated shank; hence the bolt is then free to turn in the female thread in either direction.
In order to be able to tighten the fastening of the fixture against the masonry, a torque tool is used to engage the head of the bolt which is above the surface of the fixture and to turn the bolt to threadably advance the shank which is received in the masonry hole, thereby pressing the bolt head against the fixture.
To make this advance possible Kellison attaches a hollow cap to the end of the shank while Roth attaches a cylindrical housing to the end of the shank. In both cases, this creates in the hardened epoxy below the end of the shank in the drilled masonry hole a void to accommodate the advancing shank. As the shank advances into the void, the head of the bolt then presses harder against the surface of the fixture to tighten the fastening.
In Kellison, the release agent which coats the threaded shank to permit it to turn includes commercially-available waxes or greases. Kellisone's preferred release agent is PTFE (Teflon) particles dispersed throughout a grease or a grease-like lubricant. In Roth, the release agent is Teflon tape wrapped around the thread of the shank, or a wax or plastic coating applied to the thread.
The practical drawback of a release coating of the types disclosed in the Kellison and Roth patents is that they fail to take into account imperfections in commercially-available bolts having a threaded shank. These mass-produced bolts do not have a perfectly machined helical thread, for in manufacturing the bolt the shape of the thread will often vary to some degree along the length of the shank. The surfaces of the thread flanks are somewhat irregular or rough, and the actual pitch diameter of the thread varies within the allowable tolerances of standard thread specifications.
The fact that commercially-produced bolts are imperfect does not interfere with the normal uses to which these bolts are put. Thus if the bolt cooperates with a nut that turns on the threaded shank, irregularities on the surfaces of the shank thread will not prevent the nut from turning.
But when the same bolt is used for chemical anchoring in which the thread on the shank acts to mold a female thread in the epoxy surrounding the shank, then irregularities in the shank thread are reflected in the female threads even though the shank thread is thinly coated with a grease-like release agent. Similarly, when a Teflon tape is wrapped about the shank thread to serve as a release agents the tape conforms to the irregularities of the shank thread and these irregularities are reflected in the cast female thread.
Because irregularities impressed in the female thread in the epoxy surrounding the shank thread mate with irregularities in the surface of the shank thread, this interferes with the ability of the bolt to turn to tighten the fastening of the chemical anchor. Thus if there is a small projection on the surface of the shank thread, this will create a matching indentation in the female thread cast in the epoxy that will resist turning of the bolt.
Because in a typical commercially-produced bolt, irregularities on the shank thread are dispersed throughout the surface of the bolt, it becomes very difficult to turn the bolt to tighten the fastening, even when the release agent coating the shank is a lubricant.
When as in the Roth patent, the release agent is wax or plastic, it is difficult with these materials to create on the threaded shank of the bolt a barrier layer of uniform thickness on the flank surfaces of the thread, as is necessary in a releasable barrier in accordance with the present invention. Moreover, a wax coating will not survive when the wax coated bolts are stored in a heated environment as is often the case.
A drawback of grease-like release agents on anchor bolts is that when used at construction sites where holes are being drilled in concrete masonry, then concrete dust from these drilling operations is picked up by the grease and contaminate the release agent.